What event is often cited as a catalyst for the U.S. entry into the Civil War?

The attack on Fort Sumter is widely recognized as a critical catalyst for the U.S. entry into the Civil War. This event occurred on April 12, 1861, when Confederate forces fired upon the Union-held fort in Charleston Harbor, South Carolina. This attack not only marked the beginning of open hostilities between the Northern states (the Union) and the Southern states (the Confederacy) but also galvanized public opinion in the North, leading to a surge in enlistment and support for the war effort. The bombardment of Fort Sumter prompted President Abraham Lincoln to call for troops to suppress the rebellion, further escalating tensions and solidifying the divide between the two regions. In this way, the attack served as the immediate trigger that propelled the nation into a full-scale civil war, setting the stage for the conflict over issues such as slavery and states' rights that had been brewing for decades.